The present invention relates to a method for measuring the level of a large structure such as a bridge.
In recent construction or reconstruction of a large bridge or the like, the latter is composed of block assemblies and is assembled in such a manner that every time when each block is mounted, displacement of the thus partially constructed large structure is measured.
In construction of a bridge or the like, major sections or blocks may deflect partially or over the whole length thereof due to environmental conditions such as variation of loads. Especially in recent construction of a large bridge or the like, the span between upright bridge piers erected from the ground surface or the bottom of a river is considerable so that when individual blocks are interconnected into a unitary construction, it becomes one of technical factors in the construction to estimate the local or overall deflection of a large structure from detected deflections of the major structural blocks or from detected variations in level at specific points. Measurement of such deflections in construction of a bridge as long as, say, 1km or more, which is generally carried out during the night, will take a long period of time and many measurement steps so that the measurement and the processing of the measured data become very cumbersome.
A simple method for measuring deflections of a bridge or the like described above is a so-called water leveling method which has been widely used.
FIG. 1 is a view used to explain the general principle of the water leveling method. Measuring pipes b and c are connected to respective ends of a length of tube a. The measuring tube b is installed on a supporting stand g which is disposed at a measuring point e and has a measurement indication line f above the measuring point e while the other measuring tube c is so disposed as to be movable along a scale j installed at a reference measuring point i on the stationary side h (the ground or a main pier) with known altitude.
For measurement, operators are assigned to the measuring point e and reference measuring point i, respectively, and the measuring tube c at the reference measuring point i is moved upwardly or downwardly so that the liquid level in the measuring tube b at the measuring point e may coincide with the measurement indication line f. When the liquid level coincides with the measurement indication line f, the operator reads out the height of the liquid level in the measuring tube c from the scale j.
Thereafter the measurement is repeated in a manner substantially similar to that described above to read out a graduation. When the graduation thus measured is found to be different from the graduation obtained in the first measurement, you will know that the point e on the bridge d is displaced upwardly or downwardly by a height equal to the difference between the graduations read out in the first and second measurements.
In measurement of displacement of a bridge or the like, leveling measurements on the sides of the bridge and at a position on a center line thereof are repeated every a few to 30 meters (as needs demand) in the longitudinal direction of the bridge so that every time when the measurement is made, the operator moves the measuring tube b and the supporting stand g to the next measurement point.
In the above-mentioned method, two operators are required on the side of the measurement point e and the reference point i, respectively, and a further operator is needed to record the measurement data. Thus, this method needs the operators and a long period of measurement time. In addition, such measurements as described above are generally carried out near midnight in order to eliminate displacements caused by the solar energy during the daytime so that the measurement efficiency is very low. In addition, because reading of the coincidence of the liquid level in the measuring tube b with the measurement indication line f and the reading of the scale j are visually made by the operators so that not only measurement errors but also failure in recording the measurement data tend to occur from time to time. Furthermore, since the measurement is carried out during the night, an illumination system must be used so that the measurement operation becomes harder. Moreover, from the standpoint of operation efficiency and reliability of the measurement data, there arises the problem that the communication between the operators in order to confirm the coincidence of the liquid level in the measuring tube b with the measurement indication line f becomes difficult when the distance between the measurement point e and the reference point i is increased.
The present invention was made to overcome the above and other problems encountered in the conventional water level measurement methods and has for its object to provide a method for measuring displacements at various points on a large structure such as a bridge in an efficient manner within a short period of time with a high degree of accuracy by utilizing the water leveling method.
The above and other objects, effects and features of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.